The immune system provides a mechanism to protect the body against foreign entities such as infectious organisms or foreign antigens. Under normal conditions, the immune system is capable of recognising and eliciting an immune response against foreign entities, while largely ignoring host tissue. The ability of the immune system to ignore host tissue is known as immune tolerance. Immune tolerance also refers to a state where the immune system is adapted to ignore antigens such as transplanted foreign tissues, infected tissues and allergens.
Autoimmune disease occurs when the T cells of a host recognise and react to “self” molecules, that is, molecules produced by the cells of the host. This occurs when specific self molecules interact with proteins on the surface of T cells such that the T cells recognise the molecule as foreign and consequently elicit an immune response against the self molecule.
In tissue transplantation, non-self major histocompatibility antigen present on the foreign tissue contacts the surface of T cells, resulting in T-cell activation against the foreign antigen. This activation ultimately results in allograft or xenograft rejection by the immune system.
Immunosuppressive drugs have been used to prevent allograft rejection, and to treat autoimmune diseases. Immunosuppressive drugs such as cyclosporin A, steroids, azathioprine, anti-T-cell antibodies, rapamycin, mycophenolate mofetil, desoxyspergualine and FK506, typically have undesirable side-effects, and typically require that the subject be administered the drugs for life or at least extended periods of time, thereby placing the subject at considerable risk of conditions due to long term effects of the treatment.
It would therefore be advantageous to provide an alternative method of decreasing the immune response to an antigen in a subject.